Radiant energy such as that emitted by the sun, welding arcs, light bulbs, etc. includes infrared radiation which is invisible to the naked eye and has a wavelength of at least 750 nm. Localized heating occuring as a result of exposure to infrared radiation can cause serious health problems. For example, it is known from animal studies that overexposure to both infrared and ultraviolet radiation can result in tumors of the skin. Additionally, infrared radiation is known to decrease skin elasticity leading to premature aging.
Topical applications for protection against radiant energy, especially from the sun have focused on protection against ultraviolet radiation. Ultraviolet absorbers have been used in such compositions and sold commercially as topical sunscreens (see, for example, U.S. Pat. No. 4,592,906).
Protection against infrared radiation has focused primarily on the employment of infrared absorbers such as those disclosed in U.S. Pat. No. 3,484,467. The infrared absorbers are incorporated into devices (e.g., sunglasses and safety lenses) which are sufficiently remote from the skin surface to insure that the heat absorbed by the infrared absorbers does not elevate skin temperature. For this reason, infrared absorbers have not been incorporated into compositions for the topical application to the skin.
Infrared reflectors are compounds which reflect infrared energy. Infrared reflecting films have been used to coat windows in high energy laser systems (see, "Infrared Coatings For High Energy Laser Reflectors and Windows", Morris Braunstein, SPIE, Vol. 140, Optical Coatings--Applications and Utilization II, pp. 85-94 (1978)). They have also been used to construct transparent heat mirrors for architectural glass coatings, light bulb envelopes, protective lenses, solar heat devices and the like. (See, "Materials for Transparent Heat Mirror Coatings", G. Haacke, SPIE, Vol. 324, Optical Coatings for Energy Efficiency and Solar Applications, pp. 10-15 (1982)). All of these infrared reflecting films are coated on relatively large substrates which are obviously unsuitable for topical compositions. Therefore, there is a need for a topical composition capable of protecting the skin against infrared radiation.
Applicants have discovered that an infrared reflecting composition for topical application to the skin can be prepared from infrared reflecting materials alone or by coating fine particles of an epidermally suitable substrate such as fine particles of mica or plastics with an infrared reflecting material. The resulting topical composition is easy to use and provides significant protection against infrared radiation from the sun, high energy arc lamps and the like.
It is therefore an object of the invention to provide an infrared reflecting composition for topical application to the skin.
It is another object of the invention to provide an infrared reflecting topical composition containing fine particles of an epidermally suitable substrate coated with an infrared reflecting material.
It is a further object of the invention to provide methods of protecting the skin of warm blooded animals against exposure to infrared radiation.